Future Heatwaves in NSW from the NARCliM ensemble

Abstract

NARCliM (NSW/ACT Regional Climate Modelling project) is a regional climate modeling project for the Australian area. It provides a comprehensive dynamically downscaled climate dataset for the CORDEX-AustralAsia region at 50km resolution, with a finer 10km resolution across South-East Australia. NARCliM data is being used by the NSW and ACT governments to design their climate change adaptation plans. Data is available through the AdaptNSW website (http://climatechange.environment.nsw.gov.au/). NARCliM uses WRFv3.3 regional climate model (RCM) to perform an ensemble of simulations for the present and the projected future climate. WRF is run in three different model configurations (different combinations of physical parametrizations) that have been shown to perform well in South-East Australia and were chosen based on performance and independence. These three RCMs are simulating three different periods: 1990-2009, 2020-2040 and 2060-2080. Four different GCMs (MIROC-medres 3.2, ECHAM5, CGCM 3.1 and CSIRO mk3.0) from CMIP3 provide initial and boundary conditions for the WRF simulations. These GCMs were chosen through a process that considered model performance, independence and diversity in projected future changes. This GCM-RCM matrix gives an ensemble of 12 simulations for each period. Heatwaves are here defined using the Excess Heat Factor metric. Its characteristics, including duration, frequency and intensity, are examined. Compared to observations, the NARCliM ensemble displays a good ability to simulate heatwaves across NSW with almost all present-day biases being non-significant. By 2070, robust increases in heatwave frequency, duration and peak amplitudes are found across NSW and the ACT. Western NSW is projected to have the most significant increases in peak amplitude. Most of NSW is projected to experience about 20 more heatwave-days a year by 2070 compared to the present. In many locations this is more than a doubling of the current number of heatwave days.